Extinction and quasi-stationarity in the stochastic logistic SIS model:
A Maple module and Corrections.

A monograph dealing with extinction and quasi-stationarity in the logistic
SIS model, and written by Ingemar Nåsell, was published as Volume 2022
in the Springer Lecture Notes in Mathematics Series in 2011.
The monograph develops approximations of the quasi-stationary distribution of
the SIS model in three separate parameter regions, and also gives
approximations that are uniformly valid across all three parameter regions.
In addition, the monograph gives approximations of the expected time to
extinction from the quasi-stationary distribution and from the state one.

In the monograph, numerical evaluations are made with the aid of Maple
procedures contained in a Maple module.
As an aid for a reader who wishes to do numerical evaluations of his/her own
particular cases, we make the Maple module available
here.
This Maple module is contained in a Maple worksheet that can be fed directly
to Maple.

An unfortunate error is made in Chapter 6 of the monograph.
A consequence of this error is that the conditions for validity of several
of the approximations given in the monograph need to be changed.
We emphasize, however, that the approximations themselves are in no cases
affected by the error.
A description of the changes in validity conditions is given
here.
This description suffices for the reader who is only concerned
with the results of the analysis.

A detailed list of the changes in validity conditions is given
here.
This list also gives rederivations of two of the theorems in the monograph.
The list is written for the reader who wants to follow the detailed
mathematical derivations in the monograph.